Use of newer Gnome 3 toolbar style
On Gnome/GTK 3 systems, such as Ubuntu, Audacious stands out along with, say, LibreOffice, as having an older look to it. This is only really due to to toolbar at the top, which is the same colour as the rest of the UI. On Gnome 3 apps, such as Gedit, the toolbar is a gradient from silver to green and this shows on Ubuntu as a dark gradient. If possible, I think Audacious' look could be vastly improved by simply changing this one element.